Report of a subcommittee on the nomenclature of n-dimensional crystallography. II. Symbols for arithmetic crystal classes, Bravais classes and space groups.

The Second Report of the Subcommittee on the Nomenclature of n-Dimensional Crystallography recommends specific symbols for R-irreducible groups in 4 and higher dimensions (nD), for centrings, for Bravais classes, for arithmetic crystal classes and for space groups (space-group types). The relation with higher-dimensional crystallographic groups used for the description of aperiodic crystals is briefly discussed. The Introduction discusses the general definitions used in the Report.

Implications of SU(2) symmetry on the dynamics of population difference in the two-component atomic vapor.

We present an exact many-body solution for the dynamics of the population difference N2-N1 induced by an rf field in the two-component atomic cloud characterized by equal scattering lengths. We show that no intrinsic decoherence occurs for N2-N1, provided that the exact intrinsic SU(2) symmetry holds. Decoherence for N2-N1 arises when deviations from the symmetry exist either in the scattering lengths or in the confining potentials. We suggest testing the evolution of N2-N1 by conducting echo-type experiments.

Two-dimensional inverse problem of diffusion tomography: the approach applicable for small inclusions.

A method for solving the two-dimensional inverse problems of optical diffusion tomography is proposed. The method is especially designed for the imaging of small inclusions embedded in the backgrounds of strongly scattering media. Numerical simulations show that the results are stable with respect to external noise at the boundary of the sample. The location of an inclusion is obtained with an accuracy of the order of several photon transport mean-free paths in the medium in cases both with and without noise in the scattering data used for the solution of the inverse problem.